Sunday, September 6, 2015

[Crustacea • 2015] Notes on the Taxonomy and Ecology of Labuanium politum (De Man, 1887) (Decapoda: Sesarmidae), An Obligate Arboreal Crab on the Nipah Palm, Nypa fruticans (Arecales: Arecaceae)


 Labuanium politum from Pulau Ubin, Singapore.
Fig. 3. AH, specimens climbing and foraging on nipah leaves, ca. 2–5 m above ground.
Fig. 4. A, C, male (36.6 × 32.7 mm) (ZRC 2014.0861); E, male (36.6 × 32.7 mm) (ZRC 2014.0861); G, female (34.7 × 32.0 mm) (ZRC 2014.0861). A, in situ on nipah palm leaf; C, live specimens as photographed in the laboratory; E, G, dorsal overall views.
   Ng, Yan, Lee & Tan. 2015 || LKCNHM.nus.edu.sg

Abstract
The taxonomy of the rarely reported and poorly known arboreal sesarmid crab Labuanium politum (De Man, 1887), which is the type species of Labuanium Serène & Soh, 1970, is clarified. The species is an obligate associate of the mangrove nipah palm (Arecaceae: Nypa fruticans), hiding at the frond base during the day and feeding on the leaves at night. The species is recorded from Singapore for the first time.

Key words. Sesarmidae, Labuanium politum, taxonomy, new records, nipah palm


Habitats associated with Labuanium politum in the Loboc River, Bohol, Philippines.
Fig. 1. A, B, lower reach of the river showing nipah forest; C, base of nipah palms; D, E, Labuanium politum emerging from between the stems of the nipah palm; F, G, L. politum foraging on nipah leaves; H, L. politum male (35.5 × 32.1 mm) (ZRC 2003.0381) feeding on leaflet.
Fig. 2. A, female (37.3 × 33.5 mm) (ZRC 2003.0381); C, male (30.5 × 28.5 mm) (ZRC 2003.0381); E, frontal view; G, outer view of left chela.
  Ng, Yan, Lee & Tan. 2015 || LKCNHM.nus.edu.sg

TAXONOMY 
FAMILY SESARMIDAE DANA, 1851 

Labuanium Serène & Soh, 1970
Labuanium politum (De Man, 1887)

Fig. 1. Habitats associated with Labuanium politum in the Loboc River, Bohol, Philippines.
A, B, lower reach of the river showing nipah forest; C, base of nipah palms; D, E, Labuanium politum emerging from between the stems of the nipah palm; F, G, L. politum foraging on nipah leaves; H, L. politum male (35.5 × 32.1 mm) (ZRC 2003.0381) feeding on leaflet.
  Ng, Yan, Lee & Tan. 2015 || LKCNHM.nus.edu.sg

ECOLOGY: Arboreal crabs are well known, and a large number of species have this habit. In the Indo-West Pacific, most members of the sesarmid genera Labuanium sensu lato, Selatium Serène & Soh, 1970, and Scandarma Schubart, Liu & Cuesta, 2003, as well as some species of Parasesarma De Man, 1895, and Geosesarma De Man, 1895, occur regularly on trees (see Cumberlidge et al., 2005; Fratini et al., 2005; Godsall & Smallegange, 2011; Naruse & Ng, 2007; Ng, 1988; Schubart et al., 2003, 2009; Sivasothi, 2000; Sivasothi et al., 1993; Vannini & Ruwa, 1994; Vannini et al., 1997). These should be regarded as obligate tree-dwelling crabs. Various species of Grapsidae also have arboreal habits to varying degrees (see Fratini et al., 2005; Sivasothi, 2000; Sivasothi et al., 1993; Vannini et al., 1997). Some true freshwater crabs in Africa, South and Southeast Asia (Gecarcinucoidea) are also primarily arboreal (see Cumberlidge & Sachs, 1991; Cumberlidge et al., 2005; Ng, 1991, 1995).

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Peter K. L. Ng, Bee Yan, Lee and H. H. Tan. 2015. Notes on the Taxonomy and Ecology of Labuanium politum (De Man, 1887) (Crustacea: Decapoda: Sesarmidae), An Obligate Arboreal Crab on the Nipah Palm, Nypa fruticans (Arecales: Arecaceae).
RAFFLES BULLETIN OF ZOOLOGY. Supplement No. 31: 216–225.

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